Dennis Coyne TMT Vibration Workshop 16 October 2007

LIGO-G070624-00-M

LIGO - The Laser Interferometer Gravitational-wave Observatory

Vibration and Facility Considerations(incomplete)

Dennis CoyneTMT Vibration Workshop

16 October 2007

LIGO-G070624-00-M LLNL Seminar 2

Outline

• Ambient Environment» Seismic» Wind driven seismic» Acoustic

• Facility requirements

• Facility design

• Environment data sets

• Instrument seismic & acoustic isolation design» Initial LIGO

– Passive isolation– Active quiet hydraulic isolation– Acoustic enclosures

» Advanced LIGO– Lots of active isolation!


LIGO Observatories:LIGO Observatories:Livingston, LA and Hanford, WALivingston, LA and Hanford, WA

X-ARM

X-END STATION

@ 4 km

CORNER STATION

CHILLER YARD

LASER/VACUUM EQUIPMENT AREA (EXPERIMENTAL HALL)

HVAC AIR HANDLING EQUIPMENT

Y-ARM


LIGO First Generation Detector Limiting noise floor

Interferometry is limited by three fundamental noise sources seismic noise at the lowest

frequencies thermal noise (Brownian

motion of mirror materials, suspensions) at intermediate frequencies

shot noise at high frequencies

Many other noise sources lie beneath and must be controlled as the instrument is improved

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Building vibration requirements

• Broadband» Ground-transmitted: 2 x ambient seismic amplitude spectral

density (LIGO Standard Spectrum – LSS)» Acoustic-induced: 1 x LSS

• Narrowband» < 2 x total rms motion in LSS from 0.1 – 1.0 Hz 2.8 x 10-7 m» < 20 x total rms motion in LSS from 1.0 – 50 Hz 7 x 10-8 m

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Anthropogenic Seismic Signal

• Traced to Vitrification Plant Project, 10 km from X-end, up to 5000 workers expected during 5 year project

• E. Daw’s work

R. Schofield, Environmental Disturbances; E5, E6 and E7 Investigations, LIGO-G020252-00

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Soil Structure/Resonance

• Construction spectrum has shape of non-construction spectrum --evidence for “ground resonance” of about 10 Hz

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Wind Induced Seismic Noise

• High wind induced seismic motion on the 30 in. deep floor slab in the experimental hall» ~5 times higher ASD» Increase in spectrum is broadly from ~0.3 to ~50 Hz, though mostly

from ~0.4 to ~6 Hz» Wind at building 4 km (2.5 mi) distance was ~1/2 the speed (16 mph

compared to 33 mph)

Y-End Station Seismometer signal increase due to wind increase from 12 mph to 33 mph [R. Schofield, LHO electronic log, 1/11/2002 and LIGO-G020252-00]

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Wind Histograms

• LIGO has difficulty locking it’s interferometers reliably when the wind exceeds 25 mph» ~1% of the time in Louisiana» ~10% of the time in

Washington

R. Schofield, Environmental Disturbances; E5, E6 and E7 Investigations, LIGO-G020252-00

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Chiller isolation

• Chiller plant rotating equipment generates more vibrational energy than all other sources

• Placed Chiller plant at 300 ft from science instrument area based on available land and at this distance there isn’t a significant impact on chilled water line cost

• Predicted vibration transmission factor is 0.08 (measurement?) from chiller slab to technical slab

• Chiller equipment rotates at 60 Hz (3600 rpm) and weighs 21,400 lbs, mounted on a spring isolated skid

• Typically the foundation should be ~5 times the equipment weight to minimize vibrations

• Typical spring isolator frequencies are 4 to 5 Hz and give ~1% transmission

• If unbalance results in 0.1 g (realizable limit), then technical floor sees 80 micro-g @ 60 Hz or 6 nm

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Rotating machinery

• Isolated fan skid (5 Hz vertical and horizontal), 29 to 31 Hz (1800 rpm)

• Six air handling fans operating at corner station with in-phase, unbalanced vibrations of 0.1 g (4 with 750 lb rotors, 2 with 550 lb rotors)

• One air handling fan operating with unbalanced vibration of 0.1 g

• ~15 nm horizontal and ~100 nm vertical motion on the mechanical room floor

• Significantly attenuation between the air handling unit foundation and the technical foundation due to separation

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On-the-Instrument Vibration Sources?

• LIGO limits “noisy” operating equipment on the instrument and vacuum system to:

» Ion pumps (no turbo-pumps)» LN2 Cryo-pump/dewar (no proximate pump and “infinite” capacity external tank)

Predicted displacement spectra near Right End Station Optics Chamber (BSC9) caused by operation of Turbo-Pump TC6 (LIGO-C970091-00, Cambridge Acoustical Associates)

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More Appropriate On-the-Instrument Noise Source for TMT

• The VLT Interferometer, B. Koehler, ESO, SMACS2 Symposium, 13-16 May 1997, Toulouse


Vibration Isolation Systems

» Reduce in-band seismic motion by 4 - 6 orders of magnitude

» Large range actuation for initial alignment and drift compensation

» Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during observation


Seismic Isolation – Springs and Masses

damped springcross section


Seismic System Performance

102

100

10-2

10-4

10-6

10-8

10-10

Horizontal

Vertical

10-6

HAM stackin air

BSC stackin vacuum

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Daily Variability of Seismic Noise

PRE-ISOLATOR

REQUIREMENT

(95% of the time)

Livingston

Hanford

RMS motion in 1-3 Hz band

Dis

pla

cem

ent

(m)

daynight

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Hydraulic External Pre-Isolators (HEPI)

• Static load is supported by precision coil springs

• Bellows hydraulic pistons apply force without sliding friction, moving seals

• Laminar-flow differential valves control forces

• Working fluid is glycol/water formula (soluble, nonflammable)

• Stabilized “power supply” is remote hydraulic pump with “RC” filtering & pressure feedback control

• Fits in space now used for adjusters in existing system

K. Mason, MIT

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Active Seismic Isolation

Hydraulic ExternalPre-Isolator (HEPI)

BSC

HYDRAULICACTUATOR(HORIZONTAL)

OFFLOADSPRINGS

HYDRAULICLINES & VALVES

CROSSBEAM

PIER

BSC

HAM

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Active Seismic Isolation: How it Works

• Sensor correction extends isolation

• Low freq control with disp. sensor has typical benefits – improved linearity, hysteresis, since our sensors are better than our actuators

• Replace low freq crossover with blend

• To achieve isolation, feed information from STS-2 to correct the displacement sensor.

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HEPI Preliminary Results

• LASTI performance:» Residual motions of

2e-9 m/√Hz at critical frequencies

» Consistency of transmissibility and motion ratio indicates limits are loop gain and correction match

» Exceeds requirements


Core Optics Suspension and Control


Core Optics Installation and Alignment

Initial Alignment Requirement:100 microradians (50 goal)


What’s the Future for LIGO? Advanced LIGO

• Take advantage of new technologies and on-going R&D» Active anti-seismic system operating to lower frequencies

» Lower thermal noise suspensions and optics

» Higher laser power

» More sensitive and more flexible optical configuration

x10 better amplitude sensitivity

x1000 rate=(reach)3

1 day of Advanced LIGO

» 1 year of Initial LIGO !

Planned for FY2008 start,installation beginning 2011


Astrophysical Targets for Advanced LIGO

• Neutron star & black hole binaries

» inspiral

» merger

• Spinning neutron stars» LMXBs

» known pulsars

» previously unknown

• Supernovae

• Stochastic background» Cosmological

» Early universe

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• Render seismic noise a negligible limitation to GW searches

» Both suspension and isolation systems contribute to attenuation

» Newtonian background will dominate for frequencies less than ~15 Hz

• Reduce actuation forces on test masses

• Choose an active isolation approach:

» 3 stages of 6 degree-of-freedom each

» Hydraulic External Pre-Isolation (HEPI)

» Two Active Stages of Internal Seismic Isolation

• Increase number of passive isolation stages in suspensions

» From single suspensions in initial LIGO to quadruple suspensions for Adv. LIGO

Seismic Isolation Subsystem (SEI)


Seismic isolation

• To open Advanced LIGO band at low frequencies, a complete redesign of the seismic isolation system is needed

• Active isolation, feed forward

• Required Isolation» 10x @ 1 Hz

» 3000x @ 10 Hz

Ground X

Stage 1 X

Stage 2 X

goal


Advanced LIGO suspensions

• Quad controls prototype installed at MIT and undergoing testing

• Noise prototype in fabrication» Lowest mode predicted @ 100 Hz

Quad Noise Prototype

Dennis Coyne TMT Vibration Workshop 16 October 2007

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